// fif - a command-line tool for detecting and optionally correcting files with incorrect extensions.
// Copyright (C) 2021 Lynnesbian
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program.  If not, see <https://www.gnu.org/licenses/>.

use std::io::{stdout, BufWriter};
use std::path::{Path, PathBuf};

use cfg_if::cfg_if;
use clap::Clap;
use log::{debug, error, info, trace, warn};
use once_cell::sync::OnceCell;
#[cfg(feature = "multi-threaded")]
use rayon::prelude::*;
use smartstring::alias::String;
use walkdir::{DirEntry, WalkDir};

use crate::findings::Findings;
use crate::formats::{Format, Script};
use crate::mime_db::MimeDb;
use crate::parameters::{OutputFormat, ScanOpts};
use crate::scan_error::ScanError;
use env_logger::Env;
use std::process::exit;

mod extension_set;
mod findings;
mod formats;
mod inspectors;
mod mime_db;
mod parameters;
mod scan_error;

#[cfg(test)]
mod tests;

cfg_if! {
	if #[cfg(any(all(unix, feature = "infer-backend"), all(not(unix), not(feature = "xdg-mime-backend"))))] {
		/// A [OnceCell] holding an instance of [mime_db::MimeDb].
		static MIMEDB: OnceCell<mime_db::InferDb> = OnceCell::new();
		/// The backend being used; either "Infer" or "XDG-Mime".
		const BACKEND: &str = "Infer";
	} else {
		/// A [OnceCell] holding an instance of [mime_db::MimeDb].
		static MIMEDB: OnceCell<mime_db::XdgDb> = OnceCell::new();
		/// The backend being used; either "Infer" or "XDG-Mime".
		const BACKEND: &str = "XDG-Mime";
	}
}

#[doc(hidden)]
fn main() {
	let args: parameters::Parameters = parameters::Parameters::parse();

	let mut builder = env_logger::Builder::from_env(Env::new().filter_or("RUST_LOG", "INFO"));

	builder
		// .format(|buf, r| writeln!(buf, "{} - {}", r.level(), r.args()))
		.format_module_path(false) // don't include module in logs, as it's not necessary
		.format_timestamp(None) // don't include timestamps (unnecessary, and the feature flag is disabled anyway)
		// .target(env_logger::Target::Stdout) // log to stdout rather than stderr
		.init();

	init_db();

	debug!("Iterating directory: {:?}", args.dirs);

	let extensions = args.extensions();

	debug!("Checking files with extensions: {:?}", extensions);

	let entries = scan_directory(&args.dirs, &extensions, &args.get_scan_opts());

	if entries.is_none() {
		// no need to log anything for fatal errors - fif will already have printed something obvious like
		// "[ERROR] /fake/path: No such file or directory (os error 2)". we can assume that if this has happened, the dir
		// given as input doesn't exist or is otherwise unreadable.
		exit(exitcode::NOINPUT);
	}

	let entries = entries.unwrap();

	if entries.is_empty() {
		warn!("No files matching requested options found.");
		exit(exitcode::OK);
	}

	trace!("Found {} items to check", entries.len());

	let results: Vec<_> = scan_from_walkdir(&entries)
		.into_iter()
		.filter(
			|result| result.is_err() || !result.as_ref().unwrap().valid,
			// TODO: find a way to trace! the valid files without doing ↓
			// || if result.as_ref().unwrap().valid { trace!("{:?} is fine", result.as_ref().unwrap().file); false } else { true }
		)
		.collect();

	for result in &results {
		match result {
			Ok(r) => {
				debug!(
					"{:?} should have file extension {}",
					r.file,
					r.recommended_extension().unwrap_or_else(|| "???".into())
				)
			}
			Err(f) => warn!("Error 0uo - {}", f),
		}
	}

	if results.is_empty() {
		info!("All files have valid extensions!");
		exit(0);
	}

	match args.output_format {
		OutputFormat::Script => {
			let s = Script::new();
			if s.write_all(&results, &mut BufWriter::new(stdout().lock())).is_err() {
				error!("Failed to write to stdout.");
				exit(exitcode::IOERR);
			}
		}
		OutputFormat::Text => todo!(),
	}

	debug!("Done");
}

cfg_if! {
	if #[cfg(windows)] {
		/// Determines whether or not a file is hidden by checking its win32 file attributes.
		fn is_hidden(entry: &DirEntry) -> bool {
		use std::os::windows::prelude::*;
		std::fs::metadata(entry.path()) // try to get metadata for file
			.map_or(
				false,                             // if getting metadata/attributes fails, assume it's not hidden
				|f| f.file_attributes() & 0x2 > 0, // flag for hidden - https://docs.microsoft.com/windows/win32/fileio/file-attribute-constants
			)
		}
	} else {
		/// Determines whether or not a file is hidden by checking for a leading full stop.
		fn is_hidden(entry: &DirEntry) -> bool {
		entry
			.file_name()
			.to_str()
			.map_or(false, |f| f.starts_with('.') && f != ".")
		}
	}
}

/// Returns `true` if a file matches the given criteria. This means checking whether the file's extension appears in
/// `exts`, potentially skipping over hidden files, and so on.
fn wanted_file(entry: &DirEntry, exts: &[&str], scan_opts: &ScanOpts) -> bool {
	if entry.depth() == 0 {
		// the root directory should always be scanned.
		return true;
	}

	if !scan_opts.hidden && is_hidden(entry) {
		// skip hidden files and directories. this check is performed first because it's very lightweight.
		return false;
	}

	if entry.file_type().is_dir() {
		// always allow directories - there's no point doing file extension matching on something that isn't a file.
		return true;
	}

	let ext = extension_from_path(entry.path());

	if ext.is_none() && !scan_opts.extensionless {
		// don't scan files without extensions.
		return false;
	}

	exts.contains(&ext.unwrap().to_lowercase().as_str())
}

/// Given a file path, returns its extension, using [std::path::Path::extension].
///
/// The extension is currently [converted to a lossy string](std::ffi::OsStr::to_string_lossy), although it will
/// (eventually) in future return an OsStr instead.
// TODO: ↑
fn extension_from_path(path: &Path) -> Option<String> {
	path.extension(). // Get the path's extension
		map(|e| String::from(e.to_string_lossy())) // Convert from OsStr to String
}

/// Inspects the given entry, returning a [Findings] on success and a [ScanError] on failure.
///
/// In the event of an IO error, the returned ScanError will be of type [ScanError::File]. Otherwise, a
/// [ScanError::Mime] will be returned, meaning that the file was scanned successfully, but a mimetype could not be
/// determined.
fn scan_file(entry: &DirEntry) -> Result<Findings, ScanError> {
	// try to determine mimetype for this entry
	let result = inspectors::mime_type(MIMEDB.get().unwrap(), entry.path());

	if result.is_err() {
		// an error occurred while trying to read the file
		// error!("{}: {}", entry.path().to_string_lossy(), error);
		return Err(ScanError::File(entry.path().to_path_buf()));
	}

	let result = result.unwrap();
	if result.is_none() {
		// the file was read successfully, but we were unable to determine its mimetype
		// warn!("Couldn't determine mimetype for {}", entry.path().to_string_lossy());
		return Err(ScanError::Mime(entry.path().to_path_buf()));
	}

	let result = result.unwrap();

	// set of known extensions for the given mimetype
	let known_exts = inspectors::mime_extension_lookup(result.clone());
	// file extension for this particular file
	let entry_ext = extension_from_path(entry.path());

	let valid = match known_exts {
		// there is a known set of extensions for this mimetype, and the file has an extension
		Some(e) if entry_ext.is_some() => e.contains(&entry_ext.unwrap().to_lowercase().into()),
		// either this file has no extension, or there is no known set of extensions for this mimetype :(
		Some(_) | None => false,
	};

	Ok(Findings {
		file: entry.path().to_path_buf(),
		valid,
		mime: result,
	})
}

/// Takes a slice of [DirEntry]s and calls [scan_file] on each one, returning the results in a vector.
fn scan_from_walkdir(entries: &[DirEntry]) -> Vec<Result<Findings, ScanError>> {
	cfg_if! {
		if #[cfg(feature = "multi-threaded")] {
			// rather than using a standard par_iter, split the entries into chunks of 32 first.
			// this allows each spawned thread to handle 32 files before before closing, rather than creating a new thread for
			// each file. this leads to a pretty substantial speedup that i'm pretty substantially happy about 0u0
			entries
				.par_chunks(32) // split into chunks of 32
				.flat_map(|chunk| {
					chunk // return Vec<...> instead of Chunk<Vec<...>>
						.iter() // iter over the chunk, which is a slice of DirEntry structs
						.map(|entry| scan_file(entry))
						.collect::<Vec<_>>()
				})
				.collect()
		} else {
			entries.iter().map(|entry: &DirEntry| scan_file(entry)).collect()
		}
	}
}

/// Scans a given directory with [WalkDir], filters with [wanted_file], checks for errors, and returns a vector of
/// [DirEntry]s.
fn scan_directory(dirs: &PathBuf, exts: &Vec<&str>, scan_opts: &ScanOpts) -> Option<Vec<DirEntry>> {
	let stepper = WalkDir::new(dirs).into_iter();
	let mut probably_fatal_error = false;
	let entries: Vec<DirEntry> = stepper
		.filter_entry(|e| wanted_file(e, exts, scan_opts)) // filter out unwanted files
		.filter_map(|e| {
			if let Err(err) = &e {
				debug!("uh oh spaghettio!! {:#?}", e);
				// log errors to stdout, and remove them from the iterator
				let path = err.path().map_or("General error".into(), Path::to_string_lossy);

				if err.depth() == 0 {
					// if something goes wrong while trying to read the root directory, we're probably not going to get much done
					probably_fatal_error = true;
				}

				// TODO: is there a way to just say `map_or(x, |y| y).thing()` instead of `map_or(x.thing(), |y| y.thing())`?
				// i don't care whether i'm returning a walkdir error or an io error, i just care about whether or not it
				// implements ToString (which they both do). map_or doesn't work on trait objects though :(
				error!(
					"{}: {}",
					path,
					err.io_error().map_or(err.to_string(), |e| e.to_string())
				);
				return None;
			}
			e.ok()
		})
		.filter(|e| !e.file_type().is_dir()) // remove directories from the final list
		.collect();

	if probably_fatal_error {
		None
	} else {
		Some(entries)
	}
}

/// Initialises [MIMEDB] with a value dependent on the current backend.
fn init_db() {
	cfg_if! {
		if #[cfg(any(all(unix, feature = "infer-backend"), all(not(unix), not(feature = "xdg-mime-backend"))))] {
			MIMEDB
				.set(mime_db::InferDb::init())
				.or(Err("Failed to initialise Infer backend!"))
				.unwrap();
		} else {
			MIMEDB
				.set(mime_db::XdgDb::init())
				.or(Err("Failed to initialise XDG Mime backend!"))
				.unwrap();
		}
	}
}